U.S. patent number 11,119,325 [Application Number 16/810,852] was granted by the patent office on 2021-09-14 for near eye display device.
This patent grant is currently assigned to Coretronic Corporation. The grantee listed for this patent is Coretronic Corporation. Invention is credited to Chuan-Te Cheng, Chih-Wei Shih, Chung-Ting Wei.
United States Patent |
11,119,325 |
Shih , et al. |
September 14, 2021 |
Near eye display device
Abstract
A near eye display device includes a display and a first
waveguide element, the first waveguide element including a light
incoming surface, a light exiting surface, a reflective inclined
surface and beam splitting elements. An image beam provided by the
display enters the first waveguide element via the light incoming
surface and is reflected by the reflective inclined surface in the
first waveguide element to the beam splitting elements, and is
split by the beam splitting elements and leaves the first waveguide
element via the light exiting surface. The reflective inclined
surface has a first reflectivity distribution in a first incident
angle range and a second reflectivity distribution in a second
incident angle range. An angle in the second incident angle range
is greater than an angle in the first incident angle range, and the
first reflectivity distribution has a greater reflectivity average
value than the second reflectivity distribution.
Inventors: |
Shih; Chih-Wei (Hsin-Chu,
TW), Wei; Chung-Ting (Hsin-Chu, TW), Cheng;
Chuan-Te (Hsin-Chu, TW) |
Applicant: |
Name |
City |
State |
Country |
Type |
Coretronic Corporation |
Hsin-Chu |
N/A |
TW |
|
|
Assignee: |
Coretronic Corporation
(Hsin-Chu, TW)
|
Family
ID: |
1000005805104 |
Appl.
No.: |
16/810,852 |
Filed: |
March 6, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
27/0172 (20130101); G02B 27/144 (20130101) |
Current International
Class: |
G06F
3/01 (20060101); G02B 27/01 (20060101); G02B
27/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
104062760 |
|
Sep 2014 |
|
CN |
|
108873328 |
|
Nov 2018 |
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CN |
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108873329 |
|
Nov 2018 |
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CN |
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Other References
Yaakov Amitai, "P-27: A Two-Dimensional Aperture Expander for
Ultra-Compact, High-Performance Head-Worn Displays", SID 05 DIGEST,
May 2005, pp. 360-363. cited by applicant .
Hu Xinrong, et al., "Optical System Design of Head-Mounted Display
Based on Planar Waveguide of semi-Transparent Film Array" Acta
Optica Sinica, vol. 34, No. 9, Sep. 2014, pp. 0922001-1-0922001-6.
cited by applicant .
Han Xinyan, et al., "See-Through Video Glass Based on Cascaded
Waveguide Combiner." Acta Optica Sinica, vol. 25, No. 5, May 2015,
pp. 0522004-1-0522004-9. cited by applicant.
|
Primary Examiner: Subedi; Deeprose
Attorney, Agent or Firm: JCIPRNET
Claims
What is claimed is:
1. A near eye display device, comprising a display and a first
waveguide element, wherein the display is adapted to provide an
image beam; the first waveguide element comprises a first light
incoming surface, a first light exiting surface, a reflective
inclined surface and a plurality of first beam splitting elements,
wherein the image beam enters the first waveguide element via the
first light incoming surface, the image beam is reflected by the
reflective inclined surface in the first waveguide element and
transmitted to the plurality of first beam splitting elements, and
the image beam is split by the plurality of beam splitting elements
and leaves the first waveguide element via the first light exiting
surface, wherein the reflective inclined surface has a first
reflectivity distribution in a first incident angle range and a
second reflectivity distribution in a second incident angle range,
wherein an angle in the second incident angle range is greater than
an angle in the first incident angle range, a reflectivity average
value of the first reflectivity distribution is greater than a
reflectivity average value of the second reflectivity distribution,
and the first incident angle range and the second incident angle
range are each a continuous angle range, wherein reflectivities of
the first reflectivity distribution in the first incident angle
range are greater than reflectivities of the second reflectivity
distribution in the second incident angle range.
2. The near eye display device according to claim 1, wherein in the
first incident angle range, a reflectivity of the first
reflectivity distribution corresponding to a green wavelength is
less than a reflectivity corresponding to a blue wavelength, and a
reflectivity of the first reflectivity distribution corresponding
to a red wavelength is less than the reflectivity corresponding to
the green wavelength.
3. The near eye display device according to claim 1, wherein in the
first incident angle range, the first reflectivity distribution
increases as the angle in the first incident angle range
increases.
4. The near eye display device according to claim 1, wherein a
surface of each of the plurality of first beam splitting elements
is provided with a first transflective coating, a difference
between reflectivities of the first transflective coating
corresponding to red, blue and green wavelengths falls within 5% in
a third incident angle range, wherein the third incident angle
range falls in a range of 19 degrees to 41 degrees.
5. The near eye display device according to claim 4, wherein the
reflectivities of the first transflective coating corresponding to
the red, blue and green wavelengths are less than 5% in a fourth
incident angle range, wherein an angle in the third incident angle
range is smaller than an angle in the fourth incident angle range,
the fourth incident angle range is greater than or equal to 75
degrees and less than or equal to 85 degrees, and the third
incident angle range and the fourth incident angle range are each a
continuous angle range.
6. The near eye display device according to claim 1, wherein the
second reflectivity distribution falls in a range of 0% to 10%, and
the first reflectivity distribution falls in a range of 40% to
90%.
7. The near eye display device according to claim 1, wherein the
second reflectivity distribution falls in a range of 0% to 10%, and
the first reflectivity distribution falls in a range of 20% to
70%.
8. The near eye display device according to claim 1, wherein the
first incident angle range is greater than or equal to 17 degrees
and less than or equal to 43 degrees, and the second incident angle
range is greater than or equal to 70 degrees and less than or equal
to 85 degrees.
9. The near eye display device according to claim 1, further
comprising: a second waveguide element disposed between the display
and the first waveguide element, the second waveguide element
comprising a second light incoming surface, a second light exiting
surface and a plurality of second beam splitting elements, wherein
the image beam from the display enters the second waveguide element
via the second light incoming surface, is transmitted to the
plurality of second beam splitting elements, leaves the second
waveguide element via the second light exiting surface, and enters
the first waveguide element via the first light incoming
surface.
10. The near eye display device according to claim 9, wherein a
surface of each of the plurality of second beam splitting elements
is provided with a second transflective coating, a difference
between reflectivities of the second transflective coating
corresponding to red, blue and green wavelengths falls within 3% in
a fifth incident angle range, wherein the fifth incident angle
range is greater than or equal to 30 degrees and less than or equal
to 60 degrees.
11. A near eye display device, comprising a display and a first
waveguide element, wherein the display is adapted to provide an
image beam; the first waveguide element comprises a first light
incoming surface, a first light exiting surface, a reflective
inclined surface and a plurality of first beam splitting elements,
wherein the image beam enters the first waveguide element via the
first light incoming surface, the image beam is reflected by the
reflective inclined surface in the first waveguide element and
transmitted to the plurality of first beam splitting elements, and
the image beam is split by the plurality of beam splitting elements
and leaves the first waveguide element via the first light exiting
surface to be transmitted to a projection target, wherein the
reflective inclined surface has a first reflectivity distribution
in a first incident angle range and a second reflectivity
distribution in a second incident angle range; and a surface of
each of the plurality of first beam splitting elements is provided
with a first transflective coating, a difference between
reflectivities of the first transflective coating corresponding to
red, blue and green wavelengths falls within 5% in a third incident
angle range, wherein the third incident angle range falls in a
range of 19 degrees to 48 degrees, wherein an angle in the second
incident angle range is greater than an angle in the first incident
angle range, a reflectivity average value of the first reflectivity
distribution is greater than a reflectivity average value of the
second reflectivity distribution, and the first incident angle
range and the second incident angle range are each a continuous
angle range, wherein reflectivities of the first reflectivity
distribution in the first incident angle range are greater than
reflectivities of the second reflectivity distribution in the
second incident angle range.
12. The near eye display device according to claim 11, wherein the
reflectivities of the first transflective coating corresponding to
the red, blue and green wavelengths are less than 5% in a fourth
incident angle range, wherein an angle in the third incident angle
range is smaller than an angle in the fourth incident angle range,
the fourth incident angle range is greater than or equal to 75
degrees and less than or equal to 85 degrees, and the third
incident angle range and the fourth incident angle range are each a
continuous angle range.
13. The near eye display device according to claim 11, further
comprising: a second waveguide element disposed between the display
and the first waveguide element, the second waveguide element
comprising a second light incoming surface, a second light exiting
surface and a plurality of second beam splitting elements, wherein
the image beam from the display enters the second waveguide element
via the second light incoming surface, is transmitted to the
plurality of second beam splitting elements, leaves the second
waveguide element via the second light exiting surface, and enters
the first waveguide element via the first light incoming surface;
and a surface of each of the plurality of second beam splitting
elements is provided with a second transflective coating, a
difference between reflectivities of the second transflective
coating corresponding to red, blue and green wavelengths falls
within 3% in a fifth incident angle range, wherein the fifth
incident angle range is greater than or equal to 30 degrees and
less than or equal to 60 degrees.
14. The near eye display device according to claim 11, wherein in
the first incident angle range, a reflectivity of the first
reflectivity distribution corresponding to the green wavelength is
less than a reflectivity corresponding to the blue wavelength, and
a reflectivity of the first reflectivity distribution corresponding
to the red wavelength is less than the reflectivity corresponding
to the green wavelength.
15. The near eye display device according to claim 11, wherein in
the first incident angle range, the first reflectivity distribution
increases as the angle in the first incident angle range
increases.
16. The near eye display device according to claim 11, wherein the
second reflectivity distribution falls in a range of 0% to 10%, and
the first reflectivity distribution falls in a range of 40% to
90%.
17. The near eye display device according to claim 11, wherein the
second reflectivity distribution falls in a range of 0% to 10%, and
the first reflectivity distribution falls in a range of 20% to
70%.
18. The near eye display device according to claim 11, wherein the
first incident angle range is greater than or equal to 17 degrees
and less than or equal to 43 degrees, and the second incident angle
range is greater than or equal to 70 degrees and less than or equal
to 85 degrees.
Description
BACKGROUND
Field of the Invention
The invention relates to a head-mounted display device, in
particular, to a near eye display device.
Description of Related Art
A near eye display (NED) is applied to a display system of a
head-mounted display (HMD) and is a next-generation killer product
with remarkable development potential at present. Current near eye
display technology related application may be classified into
augmented reality (AR) technology and virtual reality (VR)
technology. In terms of the augmented reality technology, relevant
developers are currently committed to providing a near eye display
with good image quality while having light weight and small
size.
In an optical architecture using the near eye display to realize
the augmented reality, an image beam for display emitted from a
projection device is reflected by an optical element with half
reflection and half penetration to enter eyes of a user. Beams for
displaying an image and external environmental beams enter the eyes
of the user, thereby achieving a display effect of the augmented
reality. However, in the process of using a traditional near eye
display, the user often encounters a problem of ghost images in a
display image. That is to say, the user sees not only an expected
image but also an unexpected image. Therefore, how to prevent ghost
images from occurring in the display image provided by the near eye
display and enable the near eye display to have favorable sight
range and visual quality so as to provide a good user experience is
one of important topics at present.
The information disclosed in this Background section is only for
enhancement of understanding of the background of the described
technology and therefore it may contain information that does not
form the prior art that is already known to a person skilled in the
art. Further, the information disclosed in the Background section
does not mean that one or more problems to be resolved by one or
more embodiments of the invention was acknowledged by a person of
ordinary skill in the art.
SUMMARY OF THE INVENTION
Embodiments of the invention provide a near eye display device
which effectively solves the problem of ghost images caused by
secondary reflection stray light and provides good display
quality.
Other objectives and advantages of the invention may be further
understood from the technical features disclosed in the
invention.
In order to achieve one or some or all of the above objectives or
other objectives, one embodiment of the invention provides a near
eye display device. The near eye display device includes a display
and a first waveguide element. The display is adapted to provide an
image beam. The first waveguide element includes a first light
incoming surface, a first light exiting surface, a reflective
inclined surface and a plurality of first beam splitting elements,
wherein the image beam enters the first waveguide element via the
first light incoming surface, and is reflected by the reflective
inclined surface in the first waveguide element to be transmitted
to the first beam splitting elements. The image beam is split by
the first beam splitting elements and leaves the first waveguide
element via the first light exiting surface. The reflective
inclined surface has a first reflectivity distribution in a first
incident angle range and a second reflectivity distribution in a
second incident angle range. An angle in the second incident angle
range is greater than an angle in the first incident angle range. A
reflectivity average value of the first reflectivity distribution
is greater than a reflectivity average value of the second
reflectivity distribution. The first incident angle range and the
second incident angle range are each a continuous angle range.
Another embodiment of the invention provides a near eye display
device. The near eye display device includes a display and a first
waveguide element. The display is adapted to provide an image beam.
The first waveguide element includes a first light incoming
surface, a first light exiting surface, a reflective inclined
surface and a plurality of first beam splitting elements, wherein
the image beam enters the first waveguide element via the first
light incoming surface, and is reflected by the reflective inclined
surface in the first waveguide element to be transmitted to the
first beam splitting elements. The image beam is split by the first
beam splitting elements and leaves the first waveguide element via
the first light exiting surface to be transmitted to a human eye.
The reflective inclined surface has a first reflectivity
distribution in a first incident angle range and a second
reflectivity distribution in a second incident angle range. A
surface of each of the plurality of first beam splitting elements
is provided with a first transflective coating. A difference
between reflectivities of the first transflective coating
corresponding to red, blue and green wavelengths in a third
incident angle range falls within 5%. The third incident angle
range falls in a range of 19 degrees to 41 degrees.
Based on the above, the near eye display device according to
embodiments of the invention is provided with the reflective
inclined surface, and the reflectivity average value of the
reflective inclined surface in the first incident angle range in
which angles are relatively small is greater than the reflectivity
average value in the second incident angle range in which angles
are relatively large, so that a situation can be avoided in which
the image beam is reflected twice on the reflective inclined
surface after entering the first waveguide element, thereby
preventing unexpected light from entering a projection target. In
addition, the near eye display device according to embodiments of
the invention is also provided with a plurality of beam splitting
elements, the surface of each of the beam splitting elements is
provided with a transflective coating, and the reflectivity of the
transflective coating is insensitive to a wavelength change within
a continuous incident angle range. Therefore, the near eye display
device according to embodiments of the invention effectively solves
the ghost image problem caused by secondary reflection stray light,
and also provides good display quality.
Other objectives, features and advantages of the invention will be
further understood from the further technological features
disclosed by the embodiments of the invention wherein there are
shown and described preferred embodiments of this invention, simply
by way of illustration of modes best suited to carry out the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
FIG. 1 is a schematic three-dimensional view showing a near eye
display device according to one embodiment of the invention.
FIG. 2 is a schematic side view showing the near eye display device
of FIG. 1.
FIG. 3 is a schematic diagram showing polarization directions of an
image beam with respect to different waveguide elements according
to one embodiment of the invention.
FIG. 4 is a schematic diagram showing ghost image light generated
by the image beam entering a waveguide element according to the
related art.
FIG. 5 is a schematic diagram showing an image beam entering a
reflective inclined surface according to one embodiment of the
invention.
FIG. 6A shows a reflectivity distribution of the reflective
inclined surface according to one embodiment of the invention.
FIG. 6B shows a reflectivity distribution of the reflective
inclined surface according to another embodiment of the
invention.
FIG. 7 is a schematic diagram showing reflection of the near eye
display device on the reflective inclined surface according to one
embodiment of the invention.
FIG. 8 is a schematic diagram showing the near eye display device
according to one embodiment of the invention.
FIG. 9A is a diagram showing a reflectivity distribution of a first
beam splitting element according to one embodiment of the
invention.
FIG. 9B is a diagram showing a reflectivity distribution of the
first beam splitting element according to one embodiment of the
invention.
FIG. 9C is a diagram showing a reflectivity distribution of the
first beam splitting element according to one embodiment of the
invention.
FIG. 10 is a diagram showing a reflectivity distribution of a
second beam splitting element according to one embodiment of the
invention.
DESCRIPTION OF THE EMBODIMENTS
In the following detailed description of the preferred embodiments,
reference is made to the accompanying drawings which form a part
hereof, and in which are shown by way of illustration specific
embodiments in which the invention may be practiced. In this
regard, directional terminology, such as "top," "bottom," "front,"
"back," etc., is used with reference to the orientation of the
Figure(s) being described. The components of the invention can be
positioned in a number of different orientations. As such, the
directional terminology is used for purposes of illustration and is
in no way limiting. On the other hand, the drawings are only
schematic and the sizes of components may be exaggerated for
clarity. It is to be understood that other embodiments may be
utilized and structural changes may be made without departing from
the scope of the invention. Also, it is to be understood that the
phraseology and terminology used herein are for the purpose of
description and should not be regarded as limiting. The use of
"including," "comprising," or "having" and variations thereof
herein is meant to encompass the items listed thereafter and
equivalents thereof as well as additional items. Unless limited
otherwise, the terms "connected," "coupled," and "mounted" and
variations thereof herein are used broadly and encompass direct and
indirect connections, couplings, and mountings. Similarly, the
terms "facing," "faces" and variations thereof herein are used
broadly and encompass direct and indirect facing, and "adjacent to"
and variations thereof herein are used broadly and encompass
directly and indirectly "adjacent to". Therefore, the description
of "A" component facing "B" component herein may contain the
situations that "A" component directly faces "B" component or one
or more additional components are between "A" component and "B"
component. Also, the description of "A" component "adjacent to" "B"
component herein may contain the situations that "A" component is
directly "adjacent to" "B" component or one or more additional
components are between "A" component and "B" component.
Accordingly, the drawings and descriptions will be regarded as
illustrative in nature and not as restrictive.
FIG. 1 is a schematic three-dimensional view showing a near eye
display device according to one embodiment of the invention. FIG. 2
is a schematic side view showing the near eye display device of
FIG. 1. Referring to FIG. 1 and FIG. 2, a near eye display device
100 of the embodiment includes a first waveguide element 110, a
second waveguide element 120, a display 130 and a lens module 140.
The display 130 is adapted to provide an image beam ML. The second
waveguide element 120 is disposed on a transmission path PA of the
image beam ML and located between the display 130 and the first
waveguide element 110. The lens module 140 is disposed between the
display 130 and the second waveguide element 120.
In the embodiment, the first waveguide element 110 is disposed on
the transmission path PA of the image beam ML and includes a first
light incoming surface S11, a first light exiting surface S12 and a
plurality of first beam splitting elements X1, X2, X3, X4, X5 and
X6 as well as a reflective inclined surface S13. The reflective
inclined surface S13 is connected with the first light incoming
surface S11, so that a junction area with an included angle .alpha.
is formed on one end portion of the first waveguide element 110.
The first waveguide element 110 extends along a first direction X,
the first beam splitting elements X1, X2, X3, X4, X5 and X6 are
arranged along the first direction X, and the number of the beam
splitting elements is not limited herein. In the embodiment, the
first light incoming surface S11 and the first light exiting
surface S12 are different portions located on the same surface of
the first waveguide element 110; however, in other embodiments,
according to the actual requirements, the first light incoming
surface S11 and the first light exiting surface S12 may be
different surfaces and the invention is not limited thereto.
The second waveguide element 120 includes a second light incoming
surface S21, a second light exiting surface S22 and a plurality of
second beam splitting elements Y1, Y2, Y3 and Y4. The second
waveguide element 120 extends along a second direction Y, and the
second beam splitting elements Y1, Y2, Y3 and Y4 are arranged along
the second direction Y. In the embodiment, the second light
incoming surface S21 and the second light exiting surface S22 are
oppositely arranged; however, in other embodiments, according to
different set positions of the display 130, the second light
incoming surface S21 may be adjacent to the second light exiting
surface S22, and the invention is not limited thereto.
In the embodiment, the first beam splitting elements X1, X2, X3,
X4, X5 and X6 as well as the second beam splitting elements Y1, Y2,
Y3 and Y4 are each provided with a half-penetration and
half-reflection coating, so the image beam ML has an optical effect
of partial penetration and partial reflection at the first beam
splitting elements X1, X2, X3, X4, X5 and X6 and the second beam
splitting elements Y1, Y2, Y3 and Y4.
Each of the above waveguide elements is, for example, made of a
transparent material and is a transparent plastic product or glass.
The number of beam splitting elements included in each waveguide
element and a space between two adjacent beam splitting elements
are designed according to different product requirements, and are
not used to limit the invention. Moreover, the number of the first
beam splitting elements may be the same as or different from the
number of the second beam splitting elements, and the space between
the adjacent beam splitting elements may be the same or different.
In the embodiment, an included angle between each beam splitting
element and the corresponding light incoming surface is generally
equal to 30 degrees or in a range of 30+/-15 degrees, or equal to
45 degrees or in a range of 45+/-15 degrees, and is designed
according to different product requirements and is not used to
limit the invention. In one embodiment, the included angle of each
beam splitting element may be equal or unequal. In addition, the
reflectivity of each beam splitting element in one embodiment is
appropriately adjusted according to an incident angle or a
wavelength.
In the embodiment, the display 130 provides the image beam ML. The
display 130, for example, includes an image projection system such
as a digital light processing (DLP) projection system, a
liquid-crystal display (LCD) projection system or a liquid crystal
on silicon (LCoS) projection system and the invention is not
limited thereto. Furthermore, the lens module 140 includes one or
more lenses or other beam transmitting elements.
In the embodiment, the image beam ML may have a single polarization
direction.
Referring to FIG. 3, FIG. 3 is a schematic diagram showing
polarization directions of an image beam with respect to different
waveguide elements according to one embodiment of the invention.
For easy illustration, an anti-reflection structure is not shown.
For example, for the second beam splitting elements Y1, Y2, Y3 and
Y4, the image beam ML entering the second waveguide element 120 is
light in the P polarization direction (like a third direction Z).
In the embodiment, the extension direction of the first waveguide
element 110 is the first direction X, and the extension direction
of the second waveguide element 120 is the second direction Y. When
the image beam ML with the P polarization direction leaves the
second waveguide element 120 and is reflected by the reflective
inclined surface S13 to be transmitted in the first waveguide
element 110, the polarization direction of the image beam ML in the
first waveguide element 110 is an S polarization direction (like a
second direction Y) for the first beam splitting elements X1, X2,
X3, X4, X5 and X6. Therefore, respective coatings of the first beam
splitting elements and the second beam splitting elements are
designed according to the image beam ML with the single
polarization direction.
Referring to FIG. 1 and FIG. 2, in the embodiment, the image beam
ML from the display 130 is transmitted along the third direction Z
in the lens module 140, passes through the lens module 140, and
enters the second waveguide element 120 via the second light
incoming surface S21 and is transmitted to the second beam
splitting elements Y1, Y2, Y3 and Y4 along the transmission path
PA. In the embodiment, a part of the image beam ML in the second
waveguide element 120 is reflected by the second beam splitting
element Y1 and a part of the image beam ML penetrates the second
beam splitting element Y1 to be transmitted along the second
direction Y, and the image beam ML leaves the second waveguide
element 120 along the third direction Z via the second light
exiting surface S22 after being reflected by the second beam
splitting elements Y1, Y2, Y3 and Y4.
Referring to FIG. 2, in the embodiment, the first waveguide element
110 and the second waveguide element 120 have a space d
therebetween in the third direction Z. More specifically, the first
light incoming surface S11 of the first waveguide element 110 and
the second light exiting surface S22 of the second waveguide
element 120 have the space d therebetween in the third direction Z.
The image beam ML continues to be transmitted along the third
direction Z after leaving the second waveguide element 120 from the
second light exiting surface S22, and passes through the space d to
enter the first waveguide element 110 from the first light incoming
surface S11 to be transmitted to the reflective inclined surface
S13. The image beam ML is transmitted to the first beam splitting
elements X1, X2, X3, X4, X5 and X6 after being reflected by the
reflective inclined surface S13. The reflective inclined surface
S13 has thereon, for example, a reflection coating which reflects
the light.
In the embodiment, the image beam ML in the first waveguide element
110 is transmitted along the first direction X. The image beam ML
leaves the first waveguide element 110 from the first light exiting
surface S12 after penetrating and being reflected by the first beam
splitting elements X1, X2, X3, X4, X5 and X6, and is projected onto
a projection target P, such as a pupil or eyes of a user. In one
embodiment, the projection target P is, for example, an image
sensing device receiving the image beam ML, such as a
charge-coupled device (CCD) or a complementary
metal-oxide-semiconductor (CMOS) image sensor.
In the embodiment, the image beam ML has a corresponding visual
angle at the projection target P. The visual angle, for example,
includes a first visual angle in the first direction X and a second
visual angle in the second direction Y. In the embodiment, the
first visual angle is determined, for example, according to the
number of the first beam splitting elements in the first waveguide
element 110, a distance from the first sheet to the last sheet of
the first beam splitting elements, or a distance between two
adjacent beam splitting elements. Similarly, the second visual
angle is determined, for example, according to the number of the
second beam splitting elements in the second waveguide element 120,
a distance from the first sheet to the last sheet of the second
beam splitting elements, or a distance between two adjacent beam
splitting elements. In the embodiment, a visual angle in a diagonal
direction of the projection target P is determined according to the
first visual angle in the first direction X and the second visual
angle in the second direction Y and is about between 20 degrees and
60 degrees. The visual angle in the diagonal direction is designed
according to different product requirements, and is not used to
limit the invention.
Based on the above, the image beam ML enters the first waveguide
element 110 and the second waveguide element 120; however, when the
image beam ML enters the reflective inclined surface S13 at a small
angle, an unexpected reflection beam is easily generated. For
example, when the image beam ML enters the reflective inclined
surface S13 at a small angle in the first waveguide element 110,
more than one reflection beam occurs on the reflective inclined
surface S13.
Referring to FIG. 4, FIG. 4 is a schematic diagram showing ghost
image light generated by the image beam entering a waveguide
element according to the related art. In the embodiment, a
waveguide element 410 is taken as an example. In the embodiment,
the waveguide element 410 adopts, for example, the structure of the
first waveguide element 110. The waveguide element 410 includes a
light incoming surface S41 and a light exiting surface S42, and the
light incoming surface S41 and the light exiting surface S42 are
located on the same surface but different positions of the
waveguide element 410. The waveguide element 410 further includes
an inclined surface S43. The inclined surface S43 has a reflective
coating which reflects an image beam ML1 and an image beam GL after
the image beam ML1 and the image beam GL enter the waveguide
element 410 via the light incoming surface S41, so that the image
beams ML1 and GL travel in the waveguide element 410. The waveguide
element 410 further includes a plurality of first beam splitting
elements X1, X2, X3, X4, X5 and X6, so that the image beam ML1 and
the image beam GL leave the waveguide element 410 via the light
exiting surface S42. The image beam ML1 is a light beam entering
the inclined surface S43 at a large angle, and is reflected only
once on the inclined surface S43, and then travels in the waveguide
element 410 and is successively reflected by the first beam
splitting elements X1, X2, X3, X4, X5 and X6 to leave the waveguide
element 410 and to generate display beams I1, I2, and the like. For
example, the display beams Il and I2 are transmitted to the eyes of
the user, so that the user sees a virtual image. The large angle
here is, for example, greater than 30 degrees or greater than 45
degrees, and the invention is not limited thereto. Those skilled in
the art may determine, according to actual situations, a suitable
range of incident angles at which reflection does not occur more
than once on the inclined surface S43.
On the other hand, the image beam GL is a light beam entering near
a junction area of the light incoming surface S41 and the inclined
surface S43, and is thus reflected more than once on the inclined
surface S43. As shown in FIG. 4, the image beam GL is transmitted
in the waveguide element 410 after being reflected twice on the
inclined surface S43 and then is reflected by the first beam
splitting elements X1, X2, X3, X4, X5 and X6 to leave the waveguide
element 410 and generate a ghost image beam such as G1. Herein, the
reason why G1 is named as ghost image beam is that the image beam
GL that is reflected twice generates light of an unexpected visual
angle, and the unexpected light continues to travel in the
waveguide element 410 and is reflected by the first beam splitting
elements X1, X2, X3, X4, X5 and X6 to enter the eyes of the user.
At this time, the user sees not only an originally expected image
but also an unexpected image. Therefore, the light that has
undergone reflection twice makes the user feel a ghost image
existing in an image when using the near eye display.
In order to reduce the ghost image in the image, in one embodiment
of the invention, reflectivity of the reflective inclined surface
S13 of the first waveguide element 110 has a first reflectivity
distribution in a first incident angle range and a second
reflectivity distribution in a second incident angle range. In the
embodiment, an angle in the second incident angle range is greater
than an angle in the first incident angle range, and a reflectivity
average value of the first reflectivity distribution is greater
than a reflectivity average value of the second reflectivity
distribution. The first incident angle range and the second
incident angle range here are each a continuous angle range.
Firstly, referring to FIG. 6A and FIG. 6B together with FIG. 5,
FIG. 5 is a schematic diagram showing an image beam entering a
reflective inclined surface according to one embodiment of the
invention. FIG. 6A shows a reflectivity distribution of the
reflective inclined surface according to one embodiment of the
invention. FIG. 6B shows a reflectivity distribution of the
reflective inclined surface according to another embodiment of the
invention. In the embodiment, different reflectivities of the
reflective inclined surface S13 change in different manners
according to light of different wavelengths. Curves 610, 620 and
630 in FIG. 6A respectively show changes of the reflectivities of
the reflective inclined surface S13 with respect to incident angle
for blue light (having a wavelength of, for example, 465 nm), green
light (having a wavelength of, for example, 525 nm), and red light
(having a wavelength of, for example, 616 nm). FIG. 6B shows the
reflectivities of the reflective inclined surface S13 different
from those of the embodiment in FIG. 6A. The curves 610, 620 and
630 in FIG. 6B respectively show changes of the reflectivities of
the reflective inclined surface S13 with respect to incident angle
for blue light (having a wavelength of, for example, 465 nm), green
light (having a wavelength of, for example, 525 nm), and red right
(having a wavelength of, for example, 616 nm). The so-called
incident angle is an angle at which the image beam enters the
reflective inclined surface S13.
In FIG. 6A, a reflectivity distribution in a first incident angle
range IA1 is called a first reflectivity distribution, and a
reflectivity distribution in a second incident angle range IA2 is
called a second reflectivity distribution. The first incident angle
range IA1 and the second incident angle range IA2 are each a
continuous angle range. The first reflectivity distribution, for
example, falls in a range of 20% to 50%. The second reflectivity
distribution, for example, falls in a range of 0% to 10%. In FIG.
6B, the first reflectivity distribution, for example, falls in a
range of 40% to 70%. The second reflectivity distribution, for
example, falls in a range of 0% to 5% or falls in a range of 0% to
10%. In other embodiments, according to different reflectivities of
the reflective inclined surface S13, the first reflectivity
distribution may, for example, fall in a range of 20% to 70%, and
the second reflectivity distribution may, for example, fall in a
range of 0% to 10%.
Referring back to FIG. 5, the image beam ML passes through the
second waveguide element 120 to enter the first waveguide element
110 along an optical axis OA. In the embodiment, the optical axis
OA is in the same direction as the third direction Z. The image
beam ML is a diffusion beam with a field of view (FOV). In FIG. 5,
light MLB1 and light MLB2 indicate edge light of the field of view
of the image beam ML in the first waveguide element 110. The light
MLB1 and light MLB2 have an angle .beta. with respect to the
optical axis, while an included angle formed between the reflective
inclined surface S13 and the first light incoming surface S11 is
.alpha.. Therefore, the light that has a major impact on the user's
viewing experience has an incident angle in a range of
.alpha.+/-.beta. with respect to the reflective inclined surface
S13. Herein, the incident angle of the image beam ML refers to an
angle at which the image beam ML enters the reflective inclined
surface S13, i.e., an included angle between the optical axis OA
and a normal of the reflective inclined surface S13.
For example, the included angle .alpha. is 30 degrees, and the
included angle .beta. is 13 degrees, so the light that mainly
enters the eyes of the user is expected to have an incident angle
falling in a range of 17 degrees to 43 degrees with respect to the
reflective inclined surface S13. On the other hand, if secondary
reflection of the light occurs on the reflective inclined surface
S13, the incident angle of the secondary reflection light is
generally large (referring again to FIG. 4), and is, for example,
greater than 70 degrees. Therefore, in the embodiment, the first
incident angle range IA1 is, for example, greater than or equal to
17 degrees and less than or equal to 43 degrees, and the second
incident angle range IA2 is, for example, greater than or equal to
70 degrees and less than or equal to 85 degrees. According to
embodiments of the invention, when the incident angle of the light
is 90 degrees, almost 100 percent of the light is reflected.
Therefore, in actual manufacturing, the reflectivity of the
reflective inclined surface S13 only allows the maximum angle of
approximately 85 degrees to cause 5% reflection.
Referring back to FIG. 6A, in the first incident angle range IA1,
the reflectivity of the first reflectivity distribution
corresponding to a green wavelength 620 is less than the
reflectivity corresponding to a blue wavelength 610. Moreover, the
reflectivity of the first reflectivity distribution corresponding
to a red wavelength 630 is less than the reflectivity thereof
corresponding to the green wavelength 620. Furthermore, the
reflectivities respectively corresponding to the blue wavelength
610, the green wavelength 620 and the red wavelength 630 increase
along with the angle in the first incident angle range IA1.
In the embodiment, the first reflectivity distribution of the
reflectivities corresponding to the blue, green and red wavelengths
610, 620 and 630 falls in a range of 20% to 50%. The average of the
reflectivity corresponding to the blue wavelength 610 in the first
incident angle range IA1 is about 36%. The average of the
reflectivity corresponding to the green wavelength 620 in the first
incident angle range IA1 is about 30%. The average of the
reflectivity corresponding to the red wavelength 630 in the first
incident angle range IA1 is about 23%.
In addition, the reflectivities corresponding to the blue, green
and red wavelengths 610, 620 and 630 in the second incident angle
range IA2 are designed to be less than 10%. In the embodiment, the
second reflectivity distribution falls in a range of 0% to 5%.
Specifically, the average of the reflectivity corresponding to the
blue wavelength 610 in the second incident angle range IA2 is about
3%. The average of the reflectivity corresponding to the green
wavelength 620 in the second incident angle range IA2 is about 1%.
The average of the reflectivity corresponding to the red wavelength
630 in the second incident angle range IA2 is about 1%. Therefore,
the reflectivity and average reflectivity in the first incident
angle range IA1 are both greater than the reflectivity and average
reflectivity in the second incident angle range IA2 regardless of
the corresponding colors. In the embodiment, the second
reflectivity distribution even falls in a range of 0% to 5%.
The embodiment of FIG. 6B is similar to that of FIG. 6A. The
difference is that the reflectivity average value of the reflective
inclined surface in the first incident angle range IA1 according to
the embodiment of FIG. 6B is designed to be greater than that of
FIG. 6A. The second reflectivity distribution selectively falls in
a range of 0% to 10% or falls in a range of 0% to 5%, and the
invention is not limited thereto. In the embodiment, the first
incident angle range IA1 is greater than or equal to 17 degrees and
less than or equal to 43 degrees, and the second incident angle
range IA2 is greater than or equal to 70 degrees and less than or
equal to 85 degrees. In the embodiment, the first reflectivity
distribution of the reflectivities corresponding to blue, green and
red wavelengths 610', 620' and 630' falls in a range of 40% to 90%.
The average of the reflectivity corresponding to the blue
wavelength 610' in the first incident angle range IA1 is about
66.5%. The average of the reflectivity corresponding to the green
wavelength 620' in the first incident angle range IA1 is about 61%.
The average of the reflectivity corresponding to the red wavelength
630' in the first incident angle range IA1 is about 44.5%. On the
other hand, the reflectivities corresponding to the blue, green and
red wavelengths 610', 620' and 630' in the second incident angle
range IA2 are far less than the reflectivity in the first incident
angle range IA1, and even fall in a range of 0% to 5% in the
embodiment. Specifically, the average of the reflectivity
corresponding to the blue wavelength 610' in the second incident
angle range IA2 is about 3%. The average of the reflectivity
corresponding to the green wavelength 620' in the second incident
angle range IA2 is about 1.8%. The average of the reflectivity
corresponding to the red wavelength 630' in the second incident
angle range IA2 is about 1.6%. Therefore, the reflectivity and
average reflectivity in the first incident angle range IA1 are both
greater than the reflectivity and average reflectivity in the
second incident angle range IA2 regardless of the corresponding
colors.
In the embodiment, similar to the change trend of the reflectivity
in the embodiment of FIG. 6A, in the first incident angle range
IA1, the reflectivity of the first reflectivity distribution
corresponding to the green wavelength 620' is less than the
reflectivity corresponding to the blue wavelength 610'. Moreover,
the reflectivity of the first reflectivity distribution
corresponding to the red wavelength 630' is less than the
reflectivity corresponding to the green wavelength 620'.
Furthermore, in FIG. 6B, the reflectivities respectively
corresponding to the blue wavelength 610', the green wavelength
620' and the red wavelength 630' increase along with the angle in
the first incident angle range IA1. However, in the invention, the
first incident angle range, the second incident angle range, the
range of the first reflectivity distribution and the range of the
second reflectivity distribution are not limited and are designed
and appropriately selected by those skilled in the art according to
actual requirements.
In the embodiments of FIG. 6A and FIG. 6B, the reflective coating
on the reflective inclined surface is, for example, formed by
stacking a plurality of various films. By utilizing thin film
interference, the reflectivity of the first incident angle range in
which angles are relatively small is greater than the reflectivity
of the second incident angle range in which angles are relatively
large. The films may be made of different materials, or may have
different reflectivities or different thicknesses, and are designed
and appropriately selected by those skilled in the art according to
common knowledge, and the descriptions thereof are omitted herein.
In addition, the forming method of the reflective coating is not
limited in the invention.
Next, referring to FIG. 7, FIG. 7 is a schematic diagram showing
reflection of the near eye display device on the reflective
inclined surface according to one embodiment of the invention. The
near eye display device illustrated in FIG. 7 is, for example, the
near eye display device 100 of FIG. 1. The reflective coating of
the reflective inclined surface S13 is any one in the embodiments
of FIG. 6A and FIG. 6B. AD on the right of FIG. 7 is a diagram
showing a distribution of the reflectivity of the reflective
inclined surface S13 with respect to different incident angles. A
first incident angle range IA1' and a second incident angle range
IA2' are each a continuous angle range. The first incident angle
range IA1' is greater than or equal to 17 degrees and less than or
equal to 43 degrees, and the second incident angle range IA2' is
greater than or equal to 70 degrees and less than or equal to 85
degrees.
The image beam ML1 and the image beam GL provided by a display (not
shown here) leave the second light exiting surface S22 of the
second waveguide element 120, pass through the space d between the
second light exiting surface S22 and the first light incoming
surface S11, and enter the first waveguide element 110 from the
first light incoming surface S11. After entering the first
waveguide element 110, the image beam ML1 is reflected once at a
point B on the reflective inclined surface S13, and then is
reflected to the first beam splitting elements X1, X2, X3, X4, X5
and X6. The incident angle of the image beam ML1 at the point B
falls in the first incident angle range IA1'. The reflectivity is,
for example, in a range of 40% to 90% or 20% to 50% or in a range
of 20% to 70%. Another image beam GL undergoes primary reflection
at a point A on the reflective inclined surface S13. The incident
angle also falls in the first incident angle range IA1'. The
reflectivity is, for example, in a range of 40% to 90% or 20% to
50% or in a range of 20% to 70%. However, the image beam GL further
undergoes secondary reflection at a point C on the reflective
inclined surface S13. The incident angle falls in the second
incident angle range IA2'. The reflectivity is less than 5%, and
the image beam GL cannot be effectively transmitted to the first
beam splitting elements X1, X2, X3, X4, X5 and X6 to enter the
projection target such as the human eye. Therefore, the reflective
inclined surface S13 of the embodiment suppresses unexpected light
generated by secondary reflection so as to avoid ghost images.
In addition, in one embodiment of the invention, a surface of each
beam splitting element in each waveguide element is provided with a
transflective coating, i.e., a half-penetration and half-reflection
coating, so that a half-penetration and half-reflection optical
effect is achieved. In embodiments of FIG. 8 to FIG. 10,
reflectivity characteristics of the reflective coating on the
surface of the beam splitting elements of the invention are
described in detail.
Firstly, referring to FIG. 8, FIG. 8 is a schematic diagram showing
the near eye display device according to one embodiment of the
invention. A near eye display device 800 includes a first waveguide
element 710 with a plurality of first beam splitting elements X1,
X2, X3, X4, X5 and X6 arranged in the first direction X and a
second waveguide element 720 with second beam splitting elements
(not shown here) arranged in the second direction Y. A surface of
each of the first beam splitting elements X1, X2, X3, X4, X5 and X6
is provided with a first transflective coating, but the
reflectivity characteristics of the first transflective coatings of
each first beam splitting element may be the same or different. For
example, the first beam splitting elements X1, X2, X3, X4, X5 and
X6 are divided into three groups C1, C2 and C3 corresponding to
three different reflectivity changes. The reflectivity
characteristics of the beam splitting elements of the three groups
C1, C2 and C3 can be seen in reference to FIG. 9A, FIG. 9B and FIG.
9C.
The grouping manner or the number of groups of a plurality of first
beam splitting elements is not limited. The reflectivity
characteristics of each group may be the same or different and be
appropriately adjusted by those skilled in the art according to the
actual situation.
FIG. 9A is a diagram showing a reflectivity distribution of a first
beam splitting element according to one embodiment of the
invention. In the embodiment, FIG. 9A shows a reflectivity change
of the group C1. The first transflective coating of the group C1
does not show significant differences between reflectivity changes
with respect to incident light of different wavelengths in a third
incident angle range IA3. In the embodiment, the third incident
angle range IA3 and a fourth incident angle range IA4 are each a
continuous angle range. The third incident angle range IA3, for
example, falls in a range of 19 degrees to 41 degrees. An angle in
the third incident angle range IA3 is smaller than an angle in the
fourth incident angle range IA4. For example, the third incident
angle range IA3 is greater than or equal to 19 degrees and less
than or equal to 41 degrees, while the fourth incident angle range
IA4 is greater than or equal to 75 degrees and less than or equal
to 85 degrees.
FIG. 9A shows a reflectivity curve 910A of blue light (for example,
corresponding to a wavelength of 449 nm), reflectivity curves 920A,
930A and 940A of three different green light (for example,
respectively corresponding to wavelengths of 520 nm, 530 nm and 550
nm), and a reflectivity curve 950A of red light (for example,
corresponding to a wavelength of 632 nm). A reflectivity
distribution in the third incident angle range IA3 falls in a range
of 7% to 16% and increases along with the angle in the third
incident angle range IA3.
The reflectivities of the first transflective coating of the group
C1 corresponding to the red wavelength 950A, the blue wavelength
910A and the green wavelengths 920A, 930A and 940A in the third
incident angle range IA3 have small differences therebetween, and
the differences between each wavelength fall in a range of 0 to 5%.
The reflectivities of the first transflective coating of the group
C1 corresponding to the red wavelength 950A, the blue wavelength
910A and the green wavelengths 920A, 930A and 940A in the fourth
incident angle range IA4 are all less than 5%. In addition, the
average of the reflectivities in the third incident angle range IA3
is greater than the reflectivity in the fourth incident angle range
IA4. The occurrence of errors are taken into consideration for the
measured values.
FIG. 9B is a diagram showing a reflectivity distribution of the
first beam splitting element according to one embodiment of the
invention. FIG. 9B shows a reflectivity change of the group C2. The
change characteristics of the reflectivity of the group C2 is
similar to the embodiment of FIG. 9A, and the difference is that
the third incident angle range IA3 is greater than or equal to 19
degrees and less than or equal to 38 degrees, while the fourth
incident angle range IA4 is greater than or equal to 75 degrees and
less than or equal to 85 degrees.
FIG. 9B shows a reflectivity curve 910B of blue light (for example,
corresponding to a wavelength of 449 nm), reflectivity curves 920B,
930B and 940B of three different green light (for example,
respectively corresponding to wavelengths of 520 nm, 530 nm and 550
nm), and a reflectivity curve 950B of red light (for example,
corresponding to a wavelength of 632 nm). The reflectivity
distribution in the third incident angle range IA3 falls in a range
of 17% to 25% and increases along with the angle in the third
incident angle range IA3.
The reflectivities of the first transflective coating of the group
C2 corresponding to the red wavelength 950B, the blue wavelength
910B and the green wavelengths 920B, 930B and 940B in the third
incident angle range IA3 have small differences therebetween, and
the differences between each wavelength fall in a range of 0 to 5%.
The reflectivities of the first transflective coating of the group
C2 corresponding to the red wavelength 950B, the blue wavelength
910B and the green wavelengths 920B, 930B and 940B in the fourth
incident angle range IA4 are all less than 5%.
FIG. 9C is a diagram showing a reflectivity distribution of the
first beam splitting element according to one embodiment of the
invention. FIG. 9C shows a reflectivity change of the group C3. The
change characteristics of the reflectivity of the group C3 is
similar to the embodiments of FIG. 9A and FIG. 9B, and the
difference is that the third incident angle range IA3 is greater
than or equal to 19 degrees and less than or equal to 28 degrees.
The fourth incident angle range IA4 is greater than or equal to 75
degrees and less than or equal to 85 degrees.
FIG. 9C shows a reflectivity curve 910C of blue light (for example,
corresponding to a wavelength of 449 nm), reflectivity curves 920C,
930C and 940C of three different green light (for example,
respectively corresponding to wavelengths of 520 nm, 530 nm and 550
nm), and a reflectivity curve 950C of red light (for example,
corresponding to a wavelength of 632 nm). The reflectivity
distribution in the third incident angle range IA3 falls in a range
of 28% to 34% and increases along with the angle in the third
incident angle range IA3.
The reflectivities of the first transflective coating of the group
C3 corresponding to the red wavelength 950C, the blue wavelength
910C and the green wavelengths 920C, 930C and 940C in the third
incident angle range IA3 have small differences therebetween, and
the differences between each wavelength fall in a range of 0 to 5%.
The reflectivities of the first transflective coating of the group
C3 corresponding to the red wavelength 950C, the blue wavelength
910C and the green wavelengths 920C, 930C and 940C in the fourth
incident angle range IA4 are all less than 5%.
Referring to FIG. 10, FIG. 10 is a diagram showing a reflectivity
distribution of a second beam splitting element according to one
embodiment of the invention. A surface of each second beam
splitting element of the second waveguide element is provided with
a second transflective coating. The second transflective coating
with the reflectivity characteristics shown in FIG. 10 is applied
to any one of the second beam splitting elements in the second
waveguide element. In the embodiment, all second beam splitting
elements in the second waveguide element have the same reflectivity
characteristics and the reflectivity characteristics shown in FIG.
10. In other embodiments, the second beam splitting elements in the
second waveguide element may have different reflectivity
characteristics from each other.
FIG. 10 shows reflectivity changes at four different incident
angles with respect to various wavelengths. A curve 1010 shows a
reflectivity change at an incident angle of 30 degrees with respect
to various wavelengths. A curve 1020 shows a reflectivity change at
an incident angle of 40 degrees with respect to various
wavelengths. A curve 1030 shows a reflectivity change at an
incident angle of 50 degrees with respect to various wavelengths. A
curve 1040 shows a reflectivity change at an incident angle of 60
degrees with respect to various wavelengths. In the embodiment, in
a fifth incident angle range, the reflectivities of the second
transflective coating corresponding to wavelengths of different
colors are very close. The fifth incident angle range is greater
than or equal to 30 degrees and less than or equal to 60 degrees.
In particular, the differences between the reflectivities
corresponding to red, blue and green light fall within 3%.
In some embodiments of the invention, the first beam splitting
element is provided with the first transflective coating. The
second beam splitting element is provided with the second
transflective coating. The differences between the reflectivities
of the first transflective coating corresponding to the red, blue
and green wavelengths in the third incident angle range fall within
5%. The third incident angle range falls in a range of 19 degrees
to 41 degrees. The differences between the reflectivities of the
second transflective coating corresponding to the red, blue and
green wavelengths in the fifth incident angle range fall within 3%.
The fifth incident angle range is greater than or equal to 30
degrees and less than or equal to 60 degrees. Therefore, the beam
splitting elements of the near eye display device according to the
embodiments of the invention appropriately control the changes of
the image beam when the image beam enters and penetrates through
the beam splitting elements at different angles. The reflectivity
is insensitive to a wavelength change, so that the image is kept
homogeneous, and good display quality is provided.
The transflective coating according to the embodiments of the
invention is, for example, formed by stacking a plurality of films.
The reflectivity change of each wavelength with respect to
different incident angles is adjusted by using thin film
interference. These films may be made of different materials, or
may have different reflectivities or different thicknesses, and are
designed and appropriately selected by those skilled in the art
according to common knowledge, and the descriptions thereof are
omitted herein. In addition, the forming method of the
transflective coating is not limited in the invention.
In summary, an exemplary embodiment of the invention provides a
near eye display device. The first waveguide element is provided
with a plurality of beam splitting elements and the reflective
inclined surface. By the reflective inclined surface, an image beam
entering the first waveguide element is reflected and transmitted
to the plurality of beam splitting elements, and is split by the
beam splitting elements to leave the first waveguide element and to
be transmitted to the projection target such as the human eye. The
reflective inclined surface has the first reflectivity distribution
in the first incident angle range and the second reflectivity
distribution in the second incident angle range. An angle in the
second incident angle range is greater than an angle in the first
incident angle range. The reflectivity average value of the first
reflectivity distribution is greater than the reflectivity average
value of the second reflectivity distribution. The first incident
angle range and the second incident angle range are each a
continuous angle range. Therefore, the reflective inclined surface
suppresses secondary reflection stray light produced by the image
beam entering near a junction area of the reflective inclined
surface and the light incoming surface, thereby reducing ghost
images in the image and providing good display quality. Another
embodiment of the invention provides a near eye display device. The
first waveguide element is provided with a plurality of beam
splitting elements and the reflective inclined surface. By the
reflective inclined surface, the image beam entering the first
waveguide element is reflected and transmitted to the plurality of
beam splitting elements, split by the beam splitting elements,
leaves the first waveguide element, and is transmitted to the human
eye. A surface of each beam splitting element is provided with a
transflective coating. The differences between the reflectivities
of the transflective coating corresponding to the red, blue and
green wavelengths fall within 5% in a specific and continuous
incident angle range. The specific and continuous incident angle
range falls in a range of 19 degrees to 41 degrees. Therefore,
according to different reflectivity requirements, the beam
splitting elements appropriately control changes of the image beam
when the image beam enters and penetrates through the beam
splitting elements at different angles. The reflectivity is
insensitive to a wavelength change, so that the image is kept
homogeneous, and good display quality is provided.
The foregoing description of the preferred embodiments of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form or to exemplary embodiments
disclosed. Accordingly, the foregoing description should be
regarded as illustrative rather than restrictive. Obviously, many
modifications and variations will be apparent to practitioners
skilled in this art. The embodiments are chosen and described in
order to best explain the principles of the invention and its best
mode practical application, thereby to enable persons skilled in
the art to understand the invention for various embodiments and
with various modifications as are suited to the particular use or
implementation contemplated. It is intended that the scope of the
invention be defined by the claims appended hereto and their
equivalents in which all terms are meant in their broadest
reasonable sense unless otherwise indicated. Therefore, the term
"the invention", "the present invention" or the like does not
necessarily limit the claim scope to a specific embodiment, and the
reference to particularly preferred exemplary embodiments of the
invention does not imply a limitation on the invention, and no such
limitation is to be inferred. The invention is limited only by the
spirit and scope of the appended claims. The abstract of the
disclosure is provided to comply with the rules requiring an
abstract, which will allow a searcher to quickly ascertain the
subject matter of the technical disclosure of any patent issued
from this disclosure. It is submitted with the understanding that
it will not be used to interpret or limit the scope or meaning of
the claims. Any advantages and benefits described may not apply to
all embodiments of the invention. It should be appreciated that
variations may be made in the embodiments described by persons
skilled in the art without departing from the scope of the
invention as defined by the following claims. Moreover, no element
and component in the disclosure is intended to be dedicated to the
public regardless of whether the element or component is explicitly
recited in the following claims.
* * * * *